Electronic control systems for managing the operation of internal combustion engines are well known and widely used in the automotive and tractor truck industries. Such systems are typically operable to control engine fueling as well as many other engine and/or vehicle operating conditions.
Designers of electronic engine control systems have heretofore devised numerous techniques for controlling engine fueling during various engine operating conditions, and one such technique is illustrated in FIG. 1. Referring to FIG. 1, a prior art technique for controlling engine fueling to thereby limit engine speed during manual gear shifting operations is illustrated, wherein such a technique is commonly referred to as progressive shift control. FIG. 1 shows a graph of engine RPM vs. vehicle speed, wherein a linear engine speed limit 10 is typically established by specifying a first engine speed limit RPM1 at a first vehicle speed VS1 and a second engine speed limit RPM2 at a second vehicle speed VS2. The engine speed limit 10 linearly increases from RPM1 to RPM2 between VS1 and VS2 and is held constant at RPM2 beyond VS2, wherein RPM2 is typically less than rated engine speed 12. Rated engine speed, also known as governed engine speed, is defined for purposes of the present invention as the engine speed at which the engine produces an advertised horsepower value.
The purpose of progressive shift control is to gradually increase available engine speed (and thus more engine power) as vehicle speed increases between VS1 and VS2, wherein typical values for VS1 and VS2 are 0.0 and 40 mph respectively. This engine speed limiting scheme accordingly encourages the vehicle operator to manually shift gears at lower engine speeds than may otherwise occur, particularly in the lower transmission gears, thereby resulting in fuel savings associated with more efficient engine operation. This feature is illustrated by gear shifting pattern 14 wherein three gear shifts are shown, each occurring at progressively increasing engine speed values.
While the progressive shift control feature 14 illustrated in FIG. 1 achieves the goal of encouraging vehicle operators to shift at lower engine speeds, it has certain drawbacks associated therewith. For example, under high engine load operating conditions, such as when traversing a grade and/or when hauling a heavily loaded trailer, providing a hard limit 10 on available engine speed can hinder the drivability of the vehicle. One example of such hindered drivability is shown by shifting pattern 16 of FIG. 1, which illustrates the effect on the shifting pattern 14 of a steep grade encountered by the same vehicle. Under such operating conditions, the limit 10 on engine speed causes the vehicle operator to shift sooner than would otherwise be preferred and the effect of the steep grade causes additional loss in both engine speed and vehicle speed over that of shifting pattern 14. Under severe operating conditions, the vehicle may accordingly have insufficient momentum to justify a shift to the next higher gear, thereby defeating the purpose of engine speed limit 10. What is needed under such conditions, is the ability to increase engine speed up to rated engine speed 12 before shifting to the next higher gear as illustrated by shifting pattern 18 in FIG. 1, wherein engine speed following a shift should ideally remain above a peak torque engine RPM 15. This scenario would improve grade climbing performance as well as the likelihood of successfully completing the shift, wherein both of these improvements result from additional kinetic energy present in the vehicle prior to the shift and from the increased engine power before and after the shift.
What is therefore needed is a system for controlling engine operation to thereby achieve the same fuel economy goals as progressive shift control while also allowing for additional engine speed only when the need therefore legitimately exists.